As someone that plays Halo, but is not part of any clan or company (call me a GDI, though I used to be part of a heavy weapons clan in H-CE for PC 10+ years ago):
- Paintball - Keep. This is kinda fun ... would like to see more map variety (The old "Timberland" map would be fantastic here)
- Sumo - Meh. It's OK.
- Groundpound arena - Keep. I have a lot of fun here. If there was a way to randomize the booster directions after X sec., that would be a nice variant.
- Mantis Breakout - Keep. This is fun, because you have to play smart to win. Personally, I'd love to see varients on this (i.e., Scorpion Breakout)
- Riftball - Keep. I like Grifball, but I like this even better.
- Minotaurs - I'm OK with this, but I only like when I'm infected. I hate the hide-n-seek mantra.
- Husky Raid - Keep. Big fan. BIG fan.
- Battle Golf - I'm a golfer, so I really enjoy this. I'd like to see more holes made, perhaps doglegs, perhaps water hazards, stroke play, etc.
- Diminishing King - This is really fun, but agree with some - additional map variations would be welcomed.
- Crazy King - Same thing ... always was a fan of the original "King of the Hill"
- Snowball Fight - This is a lot of fun ... and the map creator should be hired full time.
- Prop Hunt - I'm OK with this, but it's not my favorite, esp. when you find that one hiding spot that no one can find you.
- Skee Ball - This one we can lose. It's all random, very bouncy, and could be dialed in much better.
As for variants, my clan years ago had Hog Wars ... everyone was invisible, but everyone was given a hog. The challenge was to ram into hogs to knock the driver out, and then run them over for the kill. Whoever runs over the driver gets the kill, not necessarily the driver who rammed the hog. The invisibility is the key - yes you can be invisible, but running over an invisible player isn't easy.
I do think a custom map for Scorpion Breakout would be all sorts of fun. I think races should also be considered ... Ghost races (like the old F-Zero games), Wasp races, Banshee races, Hog races (esp. with that fast warthog). A good way to see just who is the best driver in Halo.
Again, just my 2-cents from a Level 148'er.